Wireless battery charger

ABSTRACT

A wireless battery charging system includes an inductive receiving member for receiving an AC signal for output to a matching circuit having a variable impedance with variable matching parameters. The output of the matching circuit drives a rectifier circuit for converting the inputted AC signal to a first DC voltage and having variable rectifier parameters to vary the voltage drop thereacross. A DC-to-DC converter for converting the first DC voltage to a regulated voltage for charging the battery. A current sensor senses current through the inductive receiving member, rectifier circuit and DC-to-DC converter. A controller senses the voltage drop across each of the matching circuit, rectifier circuit and DC-to-DC converter and the current there through to determine power dissipation in each of the matching circuit, rectifier circuit and DC-to-DC converter. The power distribution in each of the matching circuit, the rectifier circuit and the DC-to-DC converter can then be varied.

TECHNICAL FIELD

This application relates in general to battery chargers and, moreparticularly, battery chargers utilized in Wireless Power Transfer (WPT)systems.

BACKGROUND

Wireless charging, also known as Wireless Power Transfer (WPT), is atechnology that enables a power source to transmit electromagneticenergy to an electrical load across a gap, without interconnectingcords. Two directions for WPT are radiative wireless charging, whichtransfers energy via, for example, radiating electromagnetic,ultrasound, or acoustic waves and non-radiative charging, whichtransfers energy via an oscillating electromagnetic field.

Wireless power transmission systems can include a power transmitter unit(PTU) and power receiver unit (PRU). The transmitter can includecomponents to supply power to a transmitter resonator coil which iscoupled to a receiver resonator coil in a receiver. The receiver can becoupled to one or more loads, such as those of a mobile electronicdevice, medical device, vehicle, etc. It can be beneficial to have sometype of communication path between the receiver and the transmitter inorder to conserve efficiency.

When a PRU is associated with a device having a battery, charging thatbattery can put an undue burden on the distribution of heat across thePRU, due to converting the coupled voltage from the PTU over to theload, requiring the conversion of an alternating voltage to a regulatedDC voltage. In particular, the voltage regulation circuitry of the PRUcan be the main portion of the circuitry that dissipates heat, due tothe voltage regulation circuitry dropping the voltage from a relativelyhigh input voltage to a lower voltage when the battery is somewhatdepleted. Further, during operation, the input voltage to the PRU fromthe PTU can vary, also potentially resulting in high power dissipationin the voltage regulation circuitry of the PRU.

SUMMARY

The present invention disclosed and claimed herein, in one aspectthereof, comprises a wireless battery charging system includes aninductive receiving member for receiving an AC signal for output to amatching circuit having a variable impedance with variable matchingparameters. The output of the matching circuit drives a rectifiercircuit for converting the inputted AC signal to a first DC voltage andhaving variable rectifier parameters to vary the voltage dropthereacross. A DC-to-DC converter for converting the first DC voltage toa regulated voltage for charging the battery. A current sensor sensescurrent through the inductive receiving member, rectifier circuit andDC-to-DC converter. A controller senses the voltage drop across each ofthe matching circuit, rectifier circuit and DC-to-DC converter and thecurrent there through to determine power dissipation in each of theinductive receiving member, rectifier circuit and DC-to-DC converter.The power distribution in each of the matching circuit, the rectifiercircuit and the DC-to-DC converter can then be varied.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to thefollowing description taken in conjunction with the accompanyingDrawings in which:

FIG. 1 illustrates a diagrammatic view of a charging system for aWireless Power Transfer system;

FIG. 2 illustrates a simplified diagrammatic view of the Power ReceivingUnit interface with the battery and a device load;

FIG. 3 illustrates a block diagram of a Power Transmitting Unit and aPower Receiving Unit interface with each other to provide an overallWireless Power Transfer system;

FIG. 4 illustrates a more detailed simplified block diagram of the PowerReceiving Unit illustrating the various circuitry and the heatdissipation distribution;

FIG. 5 illustrates a diagrammatic view of an overall battery controldevice incorporating a Power Receiving Unit and a detail of theregulator embedded in the system;

FIG. 6 illustrates a block diagram of the overall Power Receiving Unit;

FIG. 7 illustrates a more detailed block diagram of the embodiment ofFIG. 6;

FIGS. 8A-8D illustrate a schematic of the Synchronous Rectifier andassociated waveforms;

FIGS. 9A and 9B and 9C illustrate schematic diagrams of the ImpedanceMatching Network;

FIG. 10 illustrates a schematic diagram of the DC-DC converter;

FIG. 11 illustrates a diagrammatic view of the voltage distributionacross the Power Receiving Unit;

FIG. 12 illustrates a flowchart depicting the overall operation of thesystem; and

FIG. 13 illustrates a flowchart depicting the overall power distributionoperation during static operation.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numbers are usedherein to designate like elements throughout, the various views andembodiments of a wireless battery charger are illustrated and described,and other possible embodiments are described. The figures are notnecessarily drawn to scale, and in some instances the drawings have beenexaggerated and/or simplified in places for illustrative purposes only.One of ordinary skill in the art will appreciate the many possibleapplications and variations based on the following examples of possibleembodiments.

Referring now to FIG. 1, there is illustrated a diagrammatic view of aWireless Power Transfer (WPT) charging system. There is provided a powertransmitter 102, which generates a driving voltage to a coil 104 whichcan be placed on a surface or in proximity to some surface. A device tobe charged 106 has a battery (not shown) associated there with that isto be charged merely by placing the device 106 within the magnetic fieldof the coil 104. As will be described hereinbelow, the device 106 has anassociated coil for interfacing with the coil 104.

As will also be disclosed herein below, when the device 106 has apartially or completely depleted battery, there may be a provision for aproximity sensor to sense the presence of the device 106 within acertain distance of the coil 104 or, alternatively, there may be aswitch on the power transmitter 102 in order to allow for activation ofthe transmitter 102 when an operation initiating a charge cycle isdesired. In typical WPT systems, the power transmitter 102 is in andidle mode and generates a Beacon that looks for some signal from thedevice 106 in an out of band communication requesting power. In a fullydepleted battery mode, this may not be possible and, thus, there must besome way for the power transmitter 102 to increase its power to a levelto at least initiate a charging cycle, as will be described in moredetail hereinbelow.

Referring now to FIG. 2, there is illustrated a block diagram of anoverall WPT system. A WPT system includes the power transmitter 102which is referred to as the Power Transmitter Unit (PTU) which drives atransmitting coil 206. The device 106 has associated therewith areceiving coil 220 for receiving a signal from the PTU 102 and whichcoil is associated with a Power Receiving Unit (PRU) 204. This PRU 204is operable to provide a DC voltage to a battery 210 which can be usedto drive a device load 228. Thus, by placing receiving coil 220 in theresonant magnetic field of the transmitter coil 206, energy will bereceived by the PRU 204 to charge the battery 210.

Referring now to FIG. 3 there is illustrated a block diagram of aWireless Power Transfer (WPT) system that includes a Power TransmittingUnit (PTU) 102 that interfaces with a Power Receiving Unit (PRU) 204.The wireless power is transferred from the PTU 102 to the PRU 204.

The PTU 102 includes a primary resonator, the coil 206, that generatesan oscillating magnetic field to wirelessly transmit power to the PRU204. A matching circuit 308 is provided for interfacing between a poweramplifier 310 and the primary resonator 206. A power supply 312 isprovided for generating power from an external source for input to thepower amplifier 310. A controller 314 is provided for controlling thepower supply 312, the power amplifier 310, and the matching circuit 308and the primary resonator 306. The controller 314 interfaces with acommunication module 316 in order to communicate with the PRU 204 over abidirectional signaling path 318.

The PRU 204 includes a secondary resonator, the coil 220, interfacingwith the primary resonator 206 of the PTU 102 via a wireless power path322. The output of the secondary resonator 220 is input to a matchingnetwork 323, referred to as an Impedance Matching Network (IMN), andthen to the input of asynchronous rectifier 324 for rectifying theoutput to a DC level, which is then input to a DC-to-DC converter 326.This comprises the output power which is then input to the device load228. It should be understood that multiple loads could be interfacedwith the DC-to-DC converter 326. A communication module 330 is operableto interface with the PTU 102 and the communication module 316associated therewith via the signaling path 318. A controller 334 isprovided on the PRU 204 for interfacing with the secondary resonator220, the rectifier 324, the communication module 130 and the DC-to-DCconverter 126.

The communication modules 316 and 330 provide for feedback signalingbetween the PRU 204 and the PTU 102 for the purpose of controlling thecharging operation. The wireless power is generated at approximately6.78 MHz of the Industrial Scientific Medical (ISM) frequency band. Thecommunication on the signaling path 318 can be facilitated, for example,over an out-of-band communication path for control signaling andoperates at the 2.4 GHz ISM band. For example, this out-of-bandcommunication path can be via Bluetooth (BLE), Wifi, or radio.Alternatively, load modulation can be provided which is referred to as“in-band communication.” This is facilitated by inducing a load on thecoil 220.

The PTU 102 can operate in multiple functional states. One functionalstate is the Configuration state in which the PTU 102 does a self-check,one is the PTU Power Save state, in which the PTU 102 periodicallydetects changes in impedance at the primary resonator and one is the PTULow Power state, in which the PTU 102 establishes a data connection withPRU(s). Another state is the PTU Power Transfer state, in which the PTU102 can regulate power transfer. Another is the Local Fault State, whichhappens when the PTU 102 experiences any local fault conditions such asover-temperature. Another is the PTU Latching Fault state, which happenswhen rogue objects are detected, or when a system error or otherfailures are reported.

The PRU 104 also has a number of functional states. One is the NullState, when the PRU 204 is under-voltage, one is the PRU Boot state,when the PRU 204 establishes a communication link with the PTU 102, oneis the PRU On state, when communication is performed, one is the PRUSystem Error State, when there is an over-voltage, over-current, orover-temperature alert, or when there is an error that has to shut downthe power.

An exemplary communication protocol, used to support wireless chargingfunctionality, can be via a Bluetooth Low Energy (BLE) link for thecontrol of power levels, identification of valid loads, and protectionof non-compliant devices. There can be three steps in the communicationprotocol, the first being device detection, the second being informationexchange, and the third being charging control. With respect to devicedetection, the PTU 102 can beacon power until a PRU 104 broadcastsadvertisements. The PTU 102 can reply to the PRU advertisements with aconnection request. The information exchange allows the PTU 102 and PRU204 to exchange their static and dynamic parameters. The chargingcontrol is initiated when the PTU 102 can provide sufficient power tomeet the demand requested from the PRU 204, or when the PRU 204 isauthorized to receive energy. With respect to situations wherein thereis insufficient charge on the PRU 204 to respond to a Beacon signal,there must be some way to force the PTU 102 to increase the amount ofpower it is transmitting, as the amount of power transmitted via thebeacon signal may be insufficient to provide sufficient power to the PRU204 for communication purposes. This operation will be described in moredetail hereinbelow.

Referring now to FIG. 4, there is illustrated a simplified block diagramof the PRU 204 illustrating the overall distribution of powerdissipation in the power delivery chain. The first lossy component isthe coil 220. This is referred to as a heat source, HS1. The coil 220incurs loss merely due to the current there through. The generatedtherein can be a function of the series resistance of the wire utilizedto form the coil 220, some magnetic misalignment of the coil 220 withrespect to the primary coil 206. In any event, this is a fixed amount ofloss resulting in heat. The second source of heat loss is the matchingnetwork 323, referred to as a heat source, HS2. The matching network 323is formed primarily of reactive components that will have some heat lossassociated therewith due to how efficiently they are configured. Thethird source of heat loss is the synchronous rectifier 324, referred toas a heat source, HS3. The last source of heat loss is the regulator326, referred to as a heat source, HS4.

In an ideal situation, the PRU 204 will have the matching network 323and the synchronous rectifier 324 designed to minimize the amount ofloss there through. Thus, if the system is operating correctly, theamount of power delivered by the PTU 102 will be reduced such that thevoltage on the input to the regular 326 is the minimum required tomaintain regulation and provide the power requested by the overallbattery 216 for charging. However, if the power is too high, there is afeedback loop through the communication channel that is required toinform the PTU 104 to either lower or raise the power. Further, therecan be other devices within the magnetic field of the coil 106,interfacing with the PTU 104 requesting power. Thus, the result is thatthere may be excess power input to the coil 220, resulting in a highervoltage at the input of the regulator 326. Of course, the regulator 326can adequately regulate the voltage or current delivered to the battery216. The result, however, is that a larger voltage drop will resultacross a regulator 326, thus resulting in a higher heat dissipation inthe regulator 326, i.e., a higher level of heat dissipated in the heatsource, HS4. The regulator 326, of course, can be designed to handlethis kind of heat load. The issue that exists, however, is furtherelaborated in the illustration of FIG. 5. The PRU 204 illustrated inFIG. 5 is defined by a boundary 502 defining, for example, theboundaries of a chip and whatever circuitry may be associated with thatchip, or even defining an enclosed and tightly populated PC board. Eachof these examples illustrates a device that will have a certain limitedcapability for dissipating heat. The possibility therefore exists thatcertain heat sources may have difficulty in dissipating heat associatedtherewith. In this illustration, the regulator 326, i.e., heat source,HS4, is illustrated in the center of the boundary 502. In practice, itis first desirable to improve the efficiency by changing the voltage atthe various points, i.e., the voltage across the Impedance MatchingNetwork, the voltage across the Synchronous Rectifier and the voltageacross the regulator 326. From a minimal control approach, to get thebest efficiencies one would design the circuit to work at the highestoutput voltage as possible and minimize the voltage drop across theregulator 326, which is a buck regulator in one embodiment. Simulationsshow the efficiency of the buck regulator 326 or DC-to-DC converterimprove when there is less voltage drop between the input and outputvoltage. The Synchronous Rectifier 324 has improved efficiencies whenthe rectified output voltage is as large as it can be. Thus, one tradeoff would be to operate at the largest output voltage as this moves allof the voltages up. A battery application, however, may be limited bythe battery voltage but if series batteries could be utilized, thiswould improve the efficiency because the output voltage can be higher.This allows operation at the highest allowable Vout to minimize the dropon the DC-to-DC stage. If that is not able to be achieved, then it isdesirable that all of the heat not be centered in this particular areaof the regulator 326 defined by the heat source. By distributing theefficiency across the various input devices between the output of thecoil and the output of the regulator 326, heat dissipation can bedistributed over the overall chip. However, in certain situations, thevoltage output by the transmitter could be excessively high and,therefore, it will be desirable not to have a high-voltage presented tothe input of the chip. In that situation, it would be desirable todistribute the heat across other circuitry or structures within theboundary 502 of the overall PRU 204. Thus, distributing the heat to thesynchronous rectifier 324 or the matching network 323 would bedesirable.

Referring now to FIG. 6, there is illustrated a more detailed diagram ofthe PRU 204. In order to distribute heat, what will be disclosed hereinis the ability to vary the configuration of both the synchronousrectifier 324 and the matching network 323 in accordance with apredetermined power distribution configuration tables. By doing so, lossis distributed to these devices in the form of a voltage drop acrossthese devices and, with knowledge of the current through the devices,the voltages across these devices and also heat dissipated through anydevice, as determined by an external heat sensor such as a thermistor todetermine device temperatures and delta device temperatures, thesubsequent power distribution in each of the devices can bedetermined/estimated. The purpose is to control the voltage drop acrossthese two devices in order to drop the voltage between the output of thecoil 220 and the input to the regulator 326, wherein the voltage to theinput of the regulator can be adjusted in order to actually control theamount of power dissipated therein. Thus, the voltage drop across theregulator 326 can be controlled at the PRU 204 somewhat independent ofthe actual voltage output of the coil 220.

The controller 334 also has a memory (not shown) associated therewith.As noted hereinabove, the controller 334 can be realized with a MicroController Unit, which has an onboard non-volatile memory such as Flashmemory associated there with. The predetermined configurationinformation is stored herein. However, the controller 334 has thecapability of adaptively changing this configuration informationdepending upon the various parameters associated with the operation ofthe device.

As illustrated in FIG. 6, the AC voltage output by the coil 220 islabeled V_(AC(RAW)) and the output of the matching network 323 islabeled V_(AC (MATCHED)). The output of the synchronous rectifier 324 islabeled with a DC voltage, V_(DC (RAW)). The Current Shunt monitorresistor 605 is provided in series between the output of the synchronousrectifier 324 and the input to the DC-to-DC converter 602, there beingtwo sensing lines 607 input to the controller 334 for sensing thedifferential voltage across this current shunt resistor 605 to providean indication of series current in the system. This is the voltage inputto the regulator 326, which is illustrated as a DC-to-DC converter 602combined with an LDO (Low-Dropout regulator). This DC-to-DC regulator602 provides a first output on a line 604 which is the LDO outputlabeled V_(DD(BLE)), which is a regulated voltage that provides thepower supply for the BLE in the communication module 330. This will bedescribed in more detail hereinbelow. A second voltage output isprovided on a line 606 from the DC-to-DC converter 602 providing asystem supply voltage is labeled V_(DD(SYS)). This second voltage outputis a regulated voltage is controlled by the operation of the DC-to-DCconverter, wherein the voltage on the output line 604 is controlled bythe linear regulator, i.e., the LDO regulator.

The operation of the overall PRU 204 is controlled by the centralcontroller 334. The central controller 334 provides both a monitoringand a control function. For monitoring, the controller 334 senses andinput from a temperature measurement device, which is formed from seriesconnected resistors 612 and an NTC resistor 614 disposed between nodes604 and ground, resistor 614 basically being a thermistor. The top endof resistor 612 is connected to node 604, as this is a regulated voltageindependent of the voltage across the battery 216 which, in a depletedstate, could be much lower than a fixed regulated voltage value. The NTCresistor 614 is disposed proximate the battery 216 for the purpose ofproviding information regarding the temperature thereof. The battery 216is connected between the line 606 and a node 608, node 608 connected toone side of the temperature sensing resistor 610, labeled R_(S), theother side of resistor 610 connected to ground. The resistor 610 is alow value resistor, the voltage thereacross providing indication of thecurrent through the battery 216. The voltage on the node 608 is sensedby the controller 334, this being a current sense input. The voltage onthe top plate of the battery 216 is also provided as an input sensedvoltage. The voltage on the input to the DC-to-DC converter 602 is alsoprovided as a sensed input voltage to the controller 334. Thus, thecontroller 334 has the ability to not only sense the voltage across theDC-to-DC converter 602, but also sense the current and voltage(V_(DD(SYS))-V_(NODE 608)) for the battery 216 and the temperature ofthe battery.

From a control standpoint, the controller 334 controls the matchingnetwork 323, the synchronous rectifier 324 and the DC-to-DC converter602, and the controller 334 can also provide messages to the PTU for thepurpose of controlling the field strength, noting that this involves amuch slower control. The matching network 323 and the synchronousrectifier 324 are all variable as to the parameters thereof such thatthe voltage drop their across can be modified. This modification is forthe purpose of actually increasing the voltage drop thereacross.

In addition, the overall device to be charged incorporating the battery216 and the PRU 204 includes an external USB interface 620 that iscomprised of a power and ground voltage lines, a voltage line, and twodata lines. This allows an external data and power source to beconnected to the device. The two data lines are input to the controller334 and the power line, on a line 622, is input to the DC-to-DCconverter 602. An additional serial communication line 624 is providedfrom the controller 334 to the system. Thus, there is provided aregulated voltage on a line 604 independent of the battery 216, whichvoltage on line 604 can be output even when the battery 216 is depletedand the voltage on node 606 is too low to power the system that canpower the BLE for communication purposes, thus preventing it fromactually powering the BLE. This voltage on node 604 will also providevoltage to the controller 334, the controller 334 typically having itsown internal LDO regulator. The serial communication line 624 isutilized to allow the controller 334 to communicate with BLEcommunication module 330. More than one communication line could beprovided to allow the controller 334 to communicate with the system.Once the battery is charged and the voltage on the battery rises above apredetermined threshold sufficient to power the system, the system canbe powered on. The system may independently power up when the voltagereaches a predefined level, all of this being under control of thesystem separate and apart from the PRU 204.

The controller 334 can be realized with a microcontroller of the type,for example, a EFM32WG230 microcontroller manufactured by Silicon Labs,Inc. This is a typical microcontroller which includes a centralized ARMprocessor, a 32-bit data bus, on board FLASH nonvolatile memory, variouscommunication interfaces, various analog interfaces such as ADCs andDACs, etc. The system also has a built-in USB interface.

From an overall operational standpoint, the controller 334 is operableto control the matching network 323 and the synchronous rectifier 324 inorder to control the voltage level to the input of the DC-to-DCconverter 602. In FIG. 7, the voltage line 604 is illustrated as beingoutput from an LDO 702. This LDO 702 can alternatively be integratedwith the DC-to-DC converter 602 or it can be separate and driven by theDC-to-DC converter 602, as illustrated in FIG. 7. There could actuallybe a bypass of the DC-to-DC converter 602 via a switch 713 in order forthe input to the LDO 702 initially to be connected to the output of thesynchronous rectifier 324. Since the power required by the BLE from line604 is relatively small, very little power loss will be incurred withinthe LDO 702. Once the voltage on the node 606 is sufficiently high,i.e., when the battery to 16 sufficiently charge, the switch 713 canswitch the input to the LDO 702 over to the output of the DC-to-DCconverter 60248 more efficient operation.

In a situation where the battery voltage on battery 216 has beendepleted below a level that can supply power to the overall device, thedevice will power down. The controller 334 will typically have some typeof power down algorithm that will allow critical data to be stored innonvolatile memory and the overall system will also do the same. Uponrestoration of power, i.e., the battery 216 being charged up to anappropriate level or an external power source being provided, both thecontroller 334 and the system will power backup in accordance with theirnormal operation. However, if no external power source is provided, itis necessary for the power to be received from the PTU 102. In theoperation of the WPT system, a minimum amount of power is required orderto drive power to the primary coil 206. Until sufficient power isdelivered thereto, potentially there would be insufficient powerdelivered to the PTU 204. However, as noted hereinabove, the WPT systemoperates in a Beacon mode, wherein the PTU 102 is activated periodicallyto generate a low level of power which is basically a request to any PRU204 that is within its magnetic field. Since the power provided in theBeacon mode may be insufficient to deliver enough power to power thecontroller 334 or the BLE in communication module 330, there must besome type of fully discharged battery protocol that is initiated at thePTU 102. (Of course, the Beacon pulse could be long enough to generatesufficient power to enable BLE communications or the PTU could extendthe Beacon pulse to a long Beacon pulse once the PTU detects animpedance change.) This protocol could be initiated based upon some typeof physical proximity sensor or some type of button that could be pushedon the PTU 102, as one example, but other techniques could be employed.Thus, during a predefined interval associated with this fully dischargedbattery protocol initiated at the PTU 102, a higher level of power isprovided on the output of the PTU 102. Again, this higher level of poweris provided before any communication link is established between the PTU102 and the PRU 204.

Operationally, this will require a power up of the controller 334 and apower up of the BLE associated with the communication module 330 at theleast. Illustrated in FIG. 7 is an isolation switch 710 disposed betweenthe output of the DC-to-DC converter 602 on a node 712 and the line 606.This will isolate the battery 216 from the output of the DC-to-DCconverter. The output of the LDO 702 powers the controller 334, whichhas an internal LDO regulator associated therewith and also the LDO 702powers a logic block 714. This logic block 714 is a block ofcombinatorial logic. In addition, the output of the DC-to-DC converteris a bypass to provide an output to the LDO 702 to provide a regulatedvoltage on the node 604 that will power the BLE on the communicationmodule 330. Since the battery 216 has been disconnected from the systemvia the switch 710 and, also, the system load 228 associated there with,there is very little current draw on the output of the DC-to-DCconverter. However, the low battery voltage on the battery 216 willactually pull the voltage on the node 606 low if connected to the node712. By isolating the battery 216 from the node 712, the system can bestabilized prior to initiating a charging operation. Further, a switch722 is provided for isolating the node 606 from the system load 228 toallow charging of a fully discharge battery prior to providing power tothe system load 228. The logic block 714 can operate on very lowvoltages and, with battery 216 being isolated by the switch 710, thevoltage on the output of the LDO 702 will increase to a level sufficientto power the controller 334 and the BLE on the communication module 330.Once this occurs, the controller 334 via the serial data bus 624 caninterface via the BLE on the communication module 330 with the PTU 102.This will allow the power to be increased to a sufficient level to beginto raise the voltage on the output of the DC-to DC converter 602 on thenode 712. This voltage is divided down by a resistor divider 724 forinput to the controller 334 and the voltage on the input to the DC-to-DCconverter 602 is divided down by a voltage divider 726 for input to thecontroller 334. The logic block 714 also receives as an input thevoltage on the node 712 to determine when to open the switch 710 batteryto be charged. The controller 334 also is allowed to communicate withthe logic block 714 to facilitate this operation.

Prior to the controller 334 being powered up, the logic block 714 willbe operable to control the switches 710 and 712. However, the matchingnetwork 323 and the synchronous rectifier 324 will operate in a staticmode such that a predefined matching impedance will be presented to thecoil 220 and the synchronous rectifier 324 will operate as aconventional synchronous rectifier, as will be described hereinbelow. Itis only when the controller 334 is powered up and charging is initiatedto the battery 216 that control of the matching network 323 and thesynchronous rectifier 324 will be facilitated. Thus, once the switch 710is open, the controller 334 will control both the matching network 323and the synchronous rectifier 324 in order to minimize the voltage dropacross the DC-to-DC converter 602 since it can measure the voltage onboth sides of the DC-to DC converter 602. This is facilitated byincreasing the voltage drop across each of the matching network 323 andthe synchronous rectifier 324. This is contrary to the normal operationof these two devices wherein they would normally be designed from astatic standpoint to provide the least loss therein, i.e., they would bedesigned for maximum efficiency. In this disclosed embodiment, asdescribed herein, the efficiency is actually decreased in order tominimize the amount of heat that is dissipated in the DC-to-DC converter602.

During charging of the battery 216, the current there through will bemonitored to minimize the current for the purpose of limiting themaximum charging current for situations wherein such batteries aslithium ion batteries are charged and also to control the temperaturethereof, which is sensed by the NTC resistor 614. Thus, the voltageacross the battery 216 will initially be very low and it will increaseas charging progresses. By sensing the voltage on the node 712 and,thus, the voltage on the node 606, the logic block 714 can determinewhen the voltage on the node 606 is sufficiently high enough to open theswitch 722 in order to provide power to the system load 228.Alternatively, the output of the DC-to-DC converter 602 could beswitched directly to connect to the system load 228 and indirectlyswitched to connect to the battery 216 through a charging circuit (notshown). In this manner, the output of the DC-to-DC converter 602 woulddrive sufficient current to the system load 228 at a sufficientlyregulated voltage and then current “metered” to the battery 216 in asufficient amount to both charge the battery 216 (keeping in mind that alithium-ion battery has a limited amount of current that can be driventhereto) and drive the system load 228, with the current and powerrequirements of the system load 228 overriding the amount of currentthat would be used to charge the battery 216. This just requires adifferent configuration of switches (not shown) to independentlydisconnect the battery 216 from the system load 228 and drive the systemload 228 directly from the DC-to-DC converter 602 independent of thecharge directed to the battery 216.

Referring now to FIG. 8A, there is illustrated a schematic diagram ofthe synchronous rectifier 324. In one embodiment, the synchronousrectifier 324 can be implemented with a half-wave rectifier. The coil220 is illustrated without the IMN 323 for illustrative purposes. The ACvoltage from the coil 220 will be input on a node 802 and a seriesN-channel transistor 804 will be disposed between the node 802 and a DCnode 806 has an output DC voltage level. The coil 220 is connectedbetween the node 802 and a ground node 810. A capacitor 812 is connectedbetween the DC node 806 and the ground node 810, and a load 816 isconnected in parallel with the capacitor 812. The transistor 804 has abody diode 818 connected in parallel therewith with the anode thereofconnected to node 802 and the cathode thereof connected to node 806.Additionally, a parallel diode could be disposed between nodes 802 and806 in a similar orientation. If the transistor 804 is turned off, thebody diode 818 will conduct when the voltage on the node 802 is higherthan the voltage on the node 806.

A zero crossing sense resistor 820 is connected on one side thereof tothe node 802 and the other end thereof is connected to the controller334. The controller 334 is thus provided the ability to determine thezero crossing of the AC input signal input to the synchronous rectifier324 and the level of the AC voltage thereon. The gate of transistor 804is controlled by the controller 334. When the voltage on the node 802rises above the voltage on the node 806, the transistor 804 is turned onby the controller 334 to charge the capacitor 812. Alternatively, thediode 818 can charge the capacitor 812 when the voltage on the node 802rises above the voltage on the node 806. When the voltage on the node802 falls below the voltage on the 806, the transistor 804 is turned offor, alternatively, the diode 818 is reverse biased and is nonconductive.

Referring now to FIG. 8B and FIG. 8C, there are illustrated waveformsfor the AC signal and the gate control voltage for the transistor 804.The AC signal input to the synchronous rectifier 324 will have zerocrossings labeled as ZC. When the crossing is positive going, this willindicate the positive half of the waveform. When the signal is negativegoing, this will indicate the negative half of the waveform. Thecontroller 334 can determine first, when the zero crossing is positivegoing and, second, when the voltage associated therewith on the node 802is greater than the voltage on the node 806. This can be sensed throughresistor 820 and also on the voltage sensing line on the input to theDC-to-DC converter 602. If a diode conducts instead of the transistor804, the diode 818 would have a self-turn on and a self-turn off andwould not require any control by the controller 334.

Thus, when the controller 334 is controlling the transistor 804, thegate voltage will be raised high at a transition 830, which will occurafter a positive going zero crossing or as close thereto as isdetermined by the controller 334 and also when the voltage on node 802is above the voltage on node 806. When the voltage on node 802 fallsbelow the voltage on node 806, the gate voltage will be pulled low at atransition 832. When the voltage on the node 802 is higher than thevoltage on the node 806, this will result in current being delivered tothe capacitor 812 during the positive half of the AC waveform. If thetransistor 804 is controlled to be conductive between transition 830 andtransition 832, this provides the most efficient operation for thesynchronous rectifier 324. If the diode were utilized during any portionof this time, this would result in a loss due to the voltage drop acrossthe diode. However, the control of the transition 804 can be varied asindicated by a dotted line 836. The dotted line 836 represents a gatevoltage transition that occurs later in time from the point at which thevoltage on node 802 exceeds the voltage on node 806 by a predeterminedamount. By controlling the width of the pulse between the transition 830to the transition 836 and, thus, the distance to the transition 832, theamount of energy transferred from the node 802 to the node 806 can bevaried. Of course, when the transistor 804 is nonconductive, the diode818 will be conductive during the time the voltage on the node 802 isabove the voltage on the node 806. Thus, the maximum loss in thesynchronous rectifier 334 in this embodiment would be the loss throughthe diode 818 when the transistor 804 is completely turned off. Furthercontrol can be provided by placing two transistors in series betweennode 802 and node 806. When both transistors are turned off, this willresult in a voltage drop of two diode voltage drops. There would be twotransistors in parallel with diodes and by controlling these twotransistors, and both transistors could be on for the most efficientoperation, one could be turned off or both could be turned off for theleast efficient operation. For example, with silicon diodes, the voltagedrop is 0.7 V. The voltage drop between node 802 and node 806 can becontrolled with the single transistor 804 to vary the voltage dropthereacross between 0.0 V and 0.7 V. With two series connectedtransistors and series connected diodes in parallel therewith, thevoltage drop thereacross can be varied between 0.0 V and 1.4 V.

Another technique that can be implemented is to have two seriesconnected transistors with the body diodes connected in oppositedirections. This will always block current when both transistors are offand thus act as an open since one of the body diodes will always be off.Using this type of connection, the DC voltage can be changed at theoutput of the synchronous rectifier by changing the duty cycle when bothtransistors are on. This provides an alternate method to change the DCvoltage at the output of the synchronous rectifier. Thus instead ofturning on both devices at the zero crossing, they are turned on “later”(smaller duty cycle) to generate a lower voltage. The maximum voltageoccurs when they are turned on at the zero crossings.

One possible issue with this technique described above is start up sincethere will not be enough voltage to control the switches. Thus, passivediode rectifiers may still be needed during start-up but could beconnected in a parallel configuration to give power to the gate-controlcircuitry while the main battery and system path is controlled by thedouble switch synchronous rectifier described above.

In an alternate embodiment, as disclosed in U.S. Pat. No. 9,384,885,issued Jul. 5, 2016, entitled Tunable Wireless Power Architectures,assigned to the present Assignee and which is incorporated by referenceherein in its entirety, an alternate and tunable synchronous rectifieris illustrated. The coil 220 is connected between a node 840 and a node842 with a series resistor 844 connected between node 842 and a groundnode 846. The IMN 323 includes, by example, and inductive element 848,in one example. The IMN 323 is connected between node 840 and a node850, the input to the synchronous rectifier 324. The synchronousrectifier 324 is comprised of two series connected transistors 852 and854 connected between a node 853 and the node 846. Transistor 854 isconnected between node 846 and the node 850 and transistor 852 isconnected between the node 846 and a node 853. The gates of transistors852 and 854 are controlled by the controller 334. A zero crossingresistor 858 is connected between the node 850 and the controller 334for sensing the voltage on the node 850 and the zero crossing point. Inoperation, when the voltage on the node 850 is above the voltage on thenode 852, transistor 852 is turned on to conduct. When the voltage onthe node 850 goes negative and falls below the voltage on the node 846,the transistor 854 is turned on to actually conduct during the negativehalf of the waveform.

It should be understood that, although a half wave rectifier isillustrated, a full wave rectifier could be realized and implemented.All that is necessary is to have the ability to control the Gates oftransistors or controllable conductive elements utilized for thesynchronous rectifier. A transistor is just one example of acontrollable conductive element.

Referring now to FIG. 9A and FIG. 9B, there is illustrated a blockdiagram of the matching network 323. The matching network 323 isconfigured, in this embodiment, with a variable capacitor 902 connectedacross the coil to 20 and a first series capacitor 904 connected to oneside of the coil 220 and a second series capacitor 906 connected to theother side of the coil 220, the two capacitors 904 and 906 beingvariable capacitors. These are illustrated in more detail in FIG. 9B,wherein the capacitors 902, 904 and 906 are realized with binaryweighted capacitors. Thus, each capacitor “bank” is comprised of aninitial value capacitor, 902′, 904′ and 906′, respectively, for each ofthe capacitors 902, 904 and 906. Each of the capacitors 902, 904 and 906will have additional capacitors that are selectively switched inparallel with its respective initial capacitor. Each of the overall bankof capacitors is binary weighted such that there will be an initialcapacitor C followed by capacitors C/2, C/4, C/8, etc. Of course, itcould be that the initial fixed capacitor could in the middle of thebinary weighted range such that the initial capacitor could be increasedor decreased. This is facilitated via a digital register 910 whichcontains a value for all of the three capacitor banks. The digital valuethat is input to the digital register 910 is received from a digital bus912 from the controller 334. However, initially the base capacitor willbe the value prior to any activation of the switches associated witheach of the capacitors in the binary weighted arrangement.

Referring now to FIG. 9C, there is illustrated an example of a receiver914 with a tunable impedance matching network 323. The receiver 914includes a resonator coil 220 coupled in series to capacitor C₁. Next,connected in parallel to the resonator coil and C₁, is a voltage sensor916 that measures voltage V₁. The differential voltage measurementsV_(c1), V_(c2) are fed into integrator INT. In embodiments, a peakdetector PD is used to detect the amplitude P (as function of time) ofthe measured voltage signal V₁. The voltage signal is also fed into amixer (SIN and COS) and one or more filters (LPF) to detect the phase ofthe voltage signal V₁. The amplitude and phase measurements can be usedby a controller to tune system components, such as the tunablecapacitors C₁, C₂, and C₃, or control other parts of the receiver, suchas rectification or safety mechanisms.

Next, coupled in parallel to the voltage sensor 916 is capacitor C₂. Acurrent sensor 918 can be positioned between voltage sensor 916 andcapacitor C₂ to measure coil current I_(coil). Coupled in series to theC₂ is a capacitor C₃. A current sensor 920 can be positioned between C₂and C₃ to measure current I₃. Each of these current sensors 918 and 920can be connected to amplitude and phase measurement circuits asdescribed above for voltage sensor 916. Coupled in series to capacitorC₃ is inductor L′₃ (balanced) and synchronous rectifier 324. Inembodiments, the synchronous rectifier 324 can be an active rectifier,such as a synchronous rectifier. The rectified voltage output V_(rect)may be fed directly to a load or though other circuitry, such as voltageclamps or filters.

In some embodiments, tunable capacitors C₁, C₂, and C₃ may be controlledby a controller or processor 922. Note that the outputs of the varioussensors 916, 918, and 920 can be fed into component 922. The controller922 in addition to some or all of components INT, PD, SIN and COS, andLPF may be integrated into an integrated circuit 924, such as an ASIC.

The input signal may be a signal representing a measured current orvoltage at a location within a power transfer system. The input signalmay be, for example, a voltage signal representing a measured current orvoltage at a location within a power transfer system, and can berepresented by A_(IN)*sin(ωt+φ), where φ is the phase of the inputsignal relative to the reference signals. For example, the input signalcan be the output of a Rogowski coil positioned within the circuitry ofa power transfer system to measure a current signal.

The signal mixers are coupled with the signal supply (such as thevoltage signal V₁) so as to receive one of the reference signals as oneinput and the input signal as another input. The mixers (SIN and COS)mix (e.g., perform time-domain multiplication) a respective referencesignal with the input signal and output mixed signal 1 and 2. Thus,mixed signal 1 can be represented by:

${Q = {{A_{IN}*{\sin\left( {{\omega\; t} + \varphi} \right)}*A*{\sin\left( {\omega\; t} \right)}} = {{\frac{{AA}_{IN}}{2}*{\cos(\varphi)}} - {\frac{{AA}_{IN}}{2}*{\cos\left( {{2\omega\; t} + \varphi} \right)}}}}},$and mixed signal 2 can be represented by:

$I = {{A_{IN}*{\sin\left( {{\omega\; t} + \varphi} \right)}*A*{\cos\left( {{\omega\; t} + \theta} \right)}} = {{\frac{{AA}_{IN}}{2}*{\sin\left( {\varphi - \theta} \right)}} + {\frac{{AA}_{IN}}{2}*{{\sin\left( {{2\omega\; t} + \varphi + \theta} \right)}.}}}}$

Filters (LPF) can be low-pass filters designed to filter, for example,the second harmonic from the first and the second mixed signal that isgenerated by the mixers. Accordingly, the filters may remove the secondorder harmonics generated from the signal mixing process as well as anyhigher order harmonics that were present in either reference signals orthe input signal. After filtering, mixed signal 1 can be represented by:

${Q = {\frac{{AA}_{IN}}{2}*\cos(\varphi)}},$and mixed signal 2 can be represented by:

$I = {\frac{{AA}_{IN}}{2}*{{\sin\left( {\varphi - \theta} \right)}.}}$

The controller receives the mixed signals Q and I, determines the phaseof the input signal, and outputs the phase of the input signal to, forexample, IMN control circuitry. Impedance at the operating frequency canbe determined using a ratio of Q to I. In embodiments, the impedance canbe input to detection algorithms such as rogue object detection, foreignobject detection, RFID detection, proximity detection, coil alignment,and the like.

Referring now to FIG. 10, there is illustrated a schematic diagram ofone example of the DC-to-DC converter 602 with the LDO bypass. The DCinput voltage is received across two nodes, a node 1002 and a groundnode 1004. This is the raw DC input voltage output by the synchronousrectifier 324. This is a buck converter for lowering the voltage. Afirst transistor switch, an N-channel transistor, 1006 is connectedbetween node 1002 and a node 1008 with a transistor 1010 connectedbetween node 1008 and the ground node 1004. Both transistors 1006 and1010 have the gates thereof controlled by a pulse width modulationcircuit 1012, both being N-channel transistors. The node 1008 isconnected to one side of a coil 1014, the other side thereof connectedto a node 1016. Node 1016 is connected to one side of a series connectedresistor 1018 and capacitor 1020 and ground node 1004. There are twofeedback controls. A voltage feedback and a current feedback. Forvoltage feedback, node 1016, the voltage output node, is input to aresistor 1024 to the input of an amplifier 1026, the other input thereofconnected to a reference voltage on a node 1028. The resistor 1024 atthe input of amplifier 1026 is connected to the top of a resistor 1030,the other side thereof connected to ground, such that the resistors 1024and 1030 provide a resistor divider to the voltage on the node 1016. Theoutput of the amplifier 1026 is selected by a switch 1032 by thecontroller for input to one input of an amplifier 1034, the other inputthereof connected to the output of oscillator 1036. The output of theamplifier 1026 provides an error voltage that is provided to theamplifier 1034 as a threshold reference level to the amplifier 1034 forcomparison to the voltage output of the oscillator 1036 to provide atriangle wave output for input to the pulse width modulator 1012. Thepulse width modulator 1012 converts this output into pulses forcontrolling the transistors 1010 and 1006.

In a current regulation mode, the current sense voltage on the node 608at the top the sense resistor 610 is provided as an input voltage to anamplifier 1040, the other input thereof connected to a reference voltage1042. These reference voltages either the node 1028 or the node 1042 canbe fixed voltages or they can be generated by the microcontroller 334.The switch 1032 is operable to select either current regulation orvoltage regulation. Initially, the system will be in a voltageregulation mode to provide an output voltage at a fixed voltage.However, during charging, it may be desirable to limit the chargingbased upon current regulation. For example, lithium-ion batteries have alimit to the amount current then can be driven thereto during charging.Thus, by using a current regulation mode, the voltage can be regulatedas a function of current rather than as a function of an absolute outputvoltage level.

Referring now to FIG. 11, there is illustrated a diagrammatic view ofthe voltage distribution from the output voltage of the coil 220 to theoutput of the regulator 602. The voltage output from the coil is a firstvoltage level, an AC voltage, 1102. This is then reduced by a voltagelevel 1104 to an AC voltage level 1106 V_(AC(MATCHED)) at the output ofthe matching network. Thus, the voltage drop across the matching networkis a voltage drop 1104. (It should be noted that this could actually bea voltage increase.) There is then another a voltage drop 1108 acrossthe synchronous rectifier resulting in output level of 1110 at theoutput of synchronous rectifier. There is then a final voltage drop 1112across the voltage regulator (DC-to-DC converter 602) to result in avoltage 1114 on the output of the voltage regulator (DC-to-DC converter602). (It should be noted that this could actually be a voltage increaseif it were a buck-boost converter.) If the configuration of both theImpedance Matching Network 323 and the Synchronous Rectifier 324 werecontrolled to obtain the maximum efficiency therefor, i.e., the smallestloss, then the voltage drops 1104 and 1108 would be defined inaccordance there with. In this case, the voltage drop 1112 across thevoltage regulator 326 would be a function of the voltage across the coil220 less the total voltage drop across the IMN 323 and the SynchronousRectifier 324. By allowing variation of the loss in the matching networkIMN 323 and the synchronous rectifier 324 to be controlled through theconfiguration thereof, this allows the controller 334 to control thevoltage drops 1104 and 1108 to minimize the voltage drop 1112 across thevoltage regulator 326. There is a minimum level that is required inorder for the regulator to operate. By reducing this voltage drop 1112to the minimum level required for the voltage regulator to operate, theamount of heat dissipated in the voltage regulator can be reduced.

Referring now to FIG. 12, there is illustrated a flowchart for theoverall operation. This is initiated at a block 1202 and then flows to adecision block 1204 to determine if the battery is below threshold ofoperation, i.e., it is a depleted battery. The program then flows to afunction block 1206 to determine if such is the case to basicallyisolate the system and the battery. As the battery is depleted, it isfirst important to power up the overall PRU 204. The program then flowsto a function block 1208 to determine if the DC voltage is abovethreshold, i.e., there is sufficient power from the Beacon mode or thebattery depletion mode of the PTU 102. If so, the program then flows toa function block 1210 to determine if the controller 334 has beenenabled, i.e., if there is sufficient voltage to allow it to operate.Again, since the system and battery have been isolated, there is nosignificant current draw other than that associated with logic block 714and the controller 334. Additionally, these circuits can be designed tooperate on very low voltages. When the controller 334 is enabled, theprogram flows to a block 1212 to then communicate with the PTU 102,i.e., there is sufficient power to both enable the controller 334 andthe BLE. The program then flows to a function block 1214 to enable thebattery charge switch, as communication with the PTU 102 will allow thePTU 102 to increase its power level. It is noted that, until there issome type of communication link, the PTU 102 will not try to drivesufficient power for any device, i.e., communication is first requiredfor any power delivery at any charging level. All the initial mode forsetting up the system does is to provide just enough power to enablecommunications and the local blocks within the PRU 204 allow the IMN 323and Synchronous Rectifier 324 and regulator 326 to be configured inorder to optimize power flow. The program then flows to a function block1216 to sense the input to the DC to DC converter for setting thevoltage drop 1112. The program then flows to a function block 1218 inorder to control the matching network and the synchronous rectifier tominimize the voltage drop 1112 by distributing the voltage drop to thematching network and synchronous rectifier via the voltage drops 1104and 1108. The program then flows to a decision block 1219 to determineif the battery voltage is above a minimum, that being the minimumrequired to power the system. If so, the program flows to a functionblock 1220 in order to enable the system switch to actually power thesystem load 228. As mentioned above, this operation can be performed inparallel to the battery charging operation with a different switchconfiguration. Once the system is in normal operating mode, as indicatedby block 1222 wherein the overall system switches to a normal batterycharging and monitoring mode, the system can operate to monitor all ofthe voltages and optimize power to the system for both charging andpowering the system load 228.

Referring now to FIG. 13, there is illustrated a flowchart depicting theoperation of the overall system will power distributed between the inputblocks. As described hereinabove, there are three blocks where in thepower dissipation therein can be adjusted. They are the IMN 323, thesynchronous rectifier 324 and the DC-to-DC converter 602. The controller334 provides control for all three of these blocks. This control isfacilitated upon knowing the input and output voltages across each ofthe blocks and the current there through in order to determine theoverall power budget that is to be distributed. The IMN 323 is basicallycomprised of passive elements and any adjustment of the values of thesepassive elements will result in internal loss therein or loss throughmismatch at the coil 220. The synchronous rectifier 324 will basicallyincur loss through the diodes, with the most lossy configuration beingthat where only the diodes are utilized as the conductive elements. TheDC-to-DC converter 602, by comparison, is a nonlinear regulator and, assuch, raising the voltage there on does not result in direct IR loss.However, there will be an increase loss as the voltage increases, whichwill result in dissipation of heat. Thus, the main control for theDC-to-DC converter 602 is control of the input voltage thereto.

The flowchart of FIG. 13 is initiated at a start block 1302 and thenproceeds to a function block 1304. The controller 334 measures thevoltage at the input to the IMN 323 at the output of the coil 220, whichis the input voltage to the synchronous rectifier 324. The output DCvoltage from the synchronous rectifier 324 is measured as well as thecurrent through the current shunt resistor 605, this being the DC inputvoltage and current to the DC-to-DC converter 602. The current throughthe current shunt resistor 605 represents the series current through theentire chain of blocks. The output voltage of the DC-to-DC converter 602is then measured on node 606. The program then proceeds to a functionblock 1306 in order to determine the power distribution from an internallookup table. The program then proceeds to a function block 1308 whereinpower distribution lookup tables are accessed from stored memory, whichstored memory is associated with the controller 334, or this memorycould be external memory (not shown).

These lookup tables are generated in accordance with differentalgorithms for different power distribution scenarios. There may bescenarios where the power distribution is evenly distributed between theblocks or unevenly distributed. There can be algorithms wherein for,higher voltages on the output of the coil 220, the power distributiondiffers. Further, a measurement of the temperature utilizing the NTC 614and be used to adjust the power distribution between the blocks (andother locations in the system can have similar temperature measuringdevices). Even further, the DC-to-DC converter 602 can be configured tooperate as a voltage mode DC-to-DC converter or as a current modeDC-to-DC converter, wherein the current can be limited through thecurrent mode configured DC-to-DC converter in accordance with a powerdistribution configuration. This will allow, for example, the currentthrough the DC-to-DC converter to be limited based upon, for example, ahigh temperature indication from the battery temperature sensor. Oncethe power distribution table is pulled up and a power distributionconfiguration is determined, then it is just a matter of the controller334 outputting the appropriate control signals to vary the configurationof the IMN 323 and change the switching control signals for thesynchronous rectifier 324 to adjust the voltage input to the DC-to-DCconverter 602 to the desired input voltage level. This is illustrated inthe three function blocks 1310, 1312 and 1314. The program then returnsback to the input of the function block 1304.

As described above, the Wireless Power Transfer system utilizes a BLE totransmit information back to the PTU from the PRU in order to adjust thepower level. However, in a straightforward and simple charge onlyoperation utilizing a “dumb” charger, there is no control of the voltageor power output by the actual PTU. All that can be done is to possiblyhave a proximity sensor that determines the proximity of the deviceassociated with the PRU being within the magnetic charging field of thePTU to turn it on or there being a user activated switch on the PTU withsome type of timeout operation. Alternatively, the device could remainin and on condition permanently. The device associated with PRU, andhaving a battery associated there with, as an example, is then placedwithin the magnetic field of the PTU and the battery charged. The systemwould work as described hereinabove with the exception that no feedbackwas provided to the PTU. Thus, no communication path is provided for.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that this wireless battery charger provides adistributed loss across the WPT circuitry in the PRU. It should beunderstood that the drawings and detailed description herein synchronousare to be regarded in an illustrative rather than a restrictive manner,and are not intended to be limiting to the particular forms and examplesdisclosed. On the contrary, included are any further modifications,changes, rearrangements, substitutions, alternatives, design choices,and embodiments apparent to those of ordinary skill in the art, withoutdeparting from the spirit and scope hereof, as defined by the followingclaims. Thus, it is intended that the following claims be interpreted toembrace all such further modifications, changes, rearrangements,substitutions, alternatives, design choices, and embodiments.

What is claimed is:
 1. A wireless battery charging system, comprising:an inductive receiving member for coupling to an inductively generatedAC signal; a matching circuit having a variable impedance for presentinga desired impedance to the inductive receiving member and havingvariable matching parameters, the matching circuit interfacing an ACsignal output by the inductive receiving member to a first AC signaloutput; a rectifier circuit for converting the first AC signal output toa first DC voltage and having variable rectifier parameters to vary afirst voltage drop thereacross; a DC-to-DC voltage converter forconverting an output of the rectifier circuit to a regulated voltagelower than the first DC voltage, an output of the DC-to-DC voltageconverter charging the battery; a current sensor for sensing seriescurrent through the matching circuit, rectifier circuit and DC-to-DCvoltage converter; a memory for storing a plurality of discretepredetermined power distribution configurations, each of the powerdistribution configurations associated with a separate powerdistribution scheme and each based on sensed voltages on an input of thematching circuit, an input of the rectifier circuit and an input of theDC-to-DC voltage converter in addition to the current sensed by thecurrent sensor as determinative factors for power distribution; and acontroller sensing a second voltage drop across each of the matchingcircuit, rectifier circuit and DC-to-DC voltage converter and thecurrent through the current sensor and determining power dissipation ineach of the matching circuit, rectifier circuit and DC-to-DC voltageconverter; and the controller adjusting the variable matching parametersin the matching circuit, the variable rectifier parameters in therectifier circuit and a voltage input to the DC-to-DC voltage converterin accordance with a predetermined power distribution configuration todistribute power thereacross in accordance with an associated powerdistribution scheme.
 2. The wireless battery charging system of claim 1,and further comprising a temperature sensor for sensing a temperature ofthe battery, the controller determining the temperature of the batteryfrom an output of the temperature sensor, and wherein the powerdistribution configuration utilizes the temperature of the battery as adeterminative factor in the power distribution scheme.
 3. The wirelessbattery charging system of claim 1, wherein the current sensor is acurrent shunt sense resistor.
 4. The wireless battery charging system ofclaim 1, and further comprising an output for driving a system load,which system load operates in parallel with the battery.
 5. The wirelessbattery charging system of claim 4 and further comprising a batterycurrent sensor for sensing current through the battery.
 6. The wirelessbattery charging system of claim 5, wherein the controller receives asan input the output of the battery current sensor and the powerdistribution configuration utilizes the current through the batterycurrent sensor as a determinative factor in the associated powerdistribution scheme.
 7. The wireless battery charging system of claim 1,wherein the DC-to-DC voltage converter can be configured as either avoltage mode DC-to-DC voltage converter or as a current mode DC-to-DCconverter.
 8. The wireless battery charging system of claim 7, whereinthe power distribution configuration can implement a power distributionscheme that configures the DC-to-DC converter as a current mode DC-to-DCvoltage converter in order to regulate a current through the DC-to-DCvoltage converter to a fixed value.
 9. The wireless battery chargingsystem of claim 1, wherein the rectifier circuit comprises asynchronousrectifier having variable rectifier parameters to vary the first voltagedrop thereacross.
 10. A wireless power delivery system, comprising: aninductive receiving member for inductively coupling to an externalinductive power transmission system; a variable impedance matchingnetwork for presenting a desired impedance to the inductive receivingmember and having variable matching parameters to output a first ACsignal output with a variable power dissipation; a rectification circuitfor rectifying the first AC signal output to a first DC voltage andhaving variable rectifier parameters to vary the power dissipatedthereby; a DC-to-DC voltage converter for converting the output of therectification circuit to a regulated voltage, the output of the DC-to-DCvoltage converter for powering an external load; a current sensor forsensing series current through the inductive receiving member,rectification circuit and DC-to-DC voltage converter; and a controllersensing a voltage drop across each of the variable impedance matchingnetwork, rectification circuit and DC-to-DC voltage converter and thecurrent through the current sensor and determining power dissipation ineach of the variable impedance matching network, rectification circuitand DC-to-DC voltage converter; the controller storing in an associatedmemory a plurality of stored power configurations, each of the storedpower configurations defining an associated power distribution schemefor configuration of each of the variable impedance matching network,rectification circuit and DC-to-DC voltage converter, wherein the sensedvoltage drop across each of the variable impedance matching network,rectification circuit in the DC-to-DC voltage converter aredeterminative factors in each of the power distribution schemes; and thecontroller selecting one of the power distribution schemes and theassociated stored power configuration and adjusting the variablematching parameters in the variable impedance matching network, thevariable rectifier parameters in the rectification circuit and a voltageinput to the DC-to-DC voltage converter in accordance with the selectedstored power configuration to distribute power thereacross in accordancewith the associated power distribution scheme.
 11. The wireless powerdelivery system of claim 10, and further comprising a temperature sensorfor sensing a temperature of the external load, the controllerdetermining the temperature of the external load from the output of thetemperature sensor, and wherein the power distribution configurationutilizes the temperature of the external load as a determinative factorin select ones of the power distribution schemes.
 12. The wireless powerdelivery system of claim 11, wherein the external load is a battery. 13.The wireless power delivery system of claim 10, wherein the DC-to-DCconverter can be configured as either a voltage mode DC-to-DC converteror as a current mode DC-to-DC converter.
 14. The wireless power deliverysystem of claim 13, wherein each of the power distributionconfigurations can implement and associated power distribution schemethat configures the DC-to-DC converter as a current mode DC-to-DCconverter in order to regulate a current through the DC-to-DC converterto a fixed value.
 15. A wireless power delivery system, comprising: acoil for inductively coupling to an external inductive powertransmission system; a variable impedance matching network forpresenting a desired impedance to the coil and having variable matchingparameters to output a first AC signal output with a variable powerdissipation; a rectification circuit for rectifying the first AC signaloutput to a first DC voltage and having variable rectifier parameters tovary the power dissipated thereby; a DC-to-DC voltage converter forconverting the output of the rectification circuit to a regulatedvoltage, the output of the DC-to-DC voltage converter for powering anexternal load; a sensor for sensing parameters of the coil, impedancematching network rectification circuit and DC-to-DC voltage converterthat are associated with heat dissipation therein; and a controllerdetermining power dissipation in each of the coil, impedance matchingnetwork, rectification circuit and DC-to-DC voltage converter; thecontroller storing a plurality of predetermined power configurations,each of the predetermined power configurations defining an associatedpower distribution scheme for configuration of each of the variableimpedance matching network, rectification circuit and DC-to-DC voltageconverter; and the controller selecting one of the power distributionschemes and the associated predetermined power configuration andadjusting the variable matching parameters in the variable impedancematching network, the variable rectifier parameters in the rectificationcircuit and the voltage input to the DC-to-DC voltage converter inaccordance with the selected predetermined power distributionconfiguration to distribute power thereacross in accordance with theassociated power distribution scheme.
 16. The wireless power deliverysystem of claim 15, wherein the sensor for at least one of the coil,rectification circuit and DC-to-DC voltage converter comprises anexternal heat sensor for determining heat dissipated by the respectiveone of the coil, rectification circuit and DC-to-DC converter.
 17. Thewireless power delivery system of claim 15, wherein the sensor includesat least a current sensor for sensing a series current through the coil,impedance matching network rectification circuit and DC-to-DC voltageconverter.
 18. The wireless power delivery system of claim 17, whereinthe controller sensing the voltage drop across each of the variableimpedance matching network, rectification circuit and DC-to-DC voltageconverter and a current through the current sensor and determining thepower dissipation in each of the variable impedance matching network,rectification circuit and DC-to-DC voltage converter.
 19. The wirelesspower delivery system of claim 15, wherein the controller adaptivelydetermines the stored predetermined power configurations.